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BMW M57 Fuel System

The BMW M57 common-rail diesel fuel system — low- and high-pressure circuits, Bosch high-pressure pump, common rail, injectors and pressure regulation.

Common-rail architecture

Injection pressure: up to 1350 bar bar — Spray pressure, original M57/DDE4.0
System split: LP + HP split — Fuel system divided into low-pressure (supply/return) and high-pressure sub-systems
Pump generation: M57 = Bosch CP1 (1st-gen common rail); M47TU / M57TU = CP3.2 (2nd-gen) — Same operating principle across generations; the fuel-system hardware differs

Component order in fuel-flow direction

LP supply chain: tank -> advance delivery pump -> outlet protection valves -> auxiliary delivery pump -> fuel filter w/ inlet pressure sensor -> LP pressure relief valve — LP supply chain
LP return chain: fuel heating (bimetal valve) -> fuel cooler -> distributor unit with throttle — LP return chain
HP chain: high-pressure pump -> rail (HP accumulator) -> pressure control valve -> rail pressure sensor -> injector — HP chain

System pressures (relative)

LP pressure (inlet): 1.5 bar < p < 5 bar bar — LP system, inlet end
LP pressure (return): p < 0.6 bar bar — LP system, return end
HP pressure: 200 bar < p < 1350 bar bar — HP system

Fuel-system design requirements

High-pressure benefit: high max injection pressure -> smaller droplets, shorter injection period
Injection timing range: > 20 deg crankshaft angle deg KW — Injection timing adjustable within broad limits; load-, speed- and temperature-dependent
Pre-injection quantity: 1-2 % of full-throttle volume % — Preliminary (pre-) injection quantity to reduce combustion noise

Advance delivery pump (EFP)

Type: roller-cell EFP, in-tank (right)
Protection valves: two outlet protection valves in tank — Prevent fuel escape in a crash/rollover

Auxiliary delivery pump

Type: in-line EFP, screw-spindle pump (high displacement); under vehicle in the inlet line to the HPP; activated in parallel with the EFP via EFP relay — M57 design
Fault effect: DDE warning lamp; power reduction above 2000 rpm (below 2000 rpm hill-climb possible; above 2000 rpm the engine would stall)

Fuel filter (13 32 2 246 070)

Part number: 13 32 2 246 070 — Fuel filter part number
Features: no fuel heating, no water separator (= M51TU filter)

Inlet (advance-delivery) pressure sensor

Damage threshold: < 1.5 bar bar — Inlet pressure below this -> possible HPP damage from inadequate fill
Stall threshold: <= 0.5 bar bar — Differential pressure (inlet vs return) at/below this -> engine can stall suddenly (pump protection)

Pressure relief valve (LP system)

Relief range: 2.0 to 3.0 bar (limiting from 2.0 bar upward) bar — Limits HPP inlet pressure to this band
Fault effect: excess pressure shortens aux-pump life; hydrodynamic noise in HPP and aux pump rises; could force the HPP shaft seal out

High-pressure pump (HPP)

Type: 3-piston radial pump with eccentric shaft — Delivery principle, both CP1 and CP3
Max pressure: 1350 bar bar — CP1 (M57) max delivery pressure
Min inlet / diff pressure: 1.9 bar / 0.5 bar bar — CP1 min inlet / differential pressure ('element filling')
Max speed / rated pressure: 3300 rpm / 1350 bar rpm / bar — CP1 max engine speed / rated pressure
Drive ratio (to crank): 4 : 3 — CP1 ratio relationship to crankshaft
Cranking output: >= 350 bar at 250 rpm bar — HPP output while cranking (chain-driven, no timing; each of 3 pistons does one stroke per pump revolution)

HPP drive / function figures

Drive: chain drive at > 1/2 engine speed (max. 3300 rpm) rpm — Drive
Suction-valve opening: 0.5-1.5 bar bar — Suction valve opening pressure
Delivery strokes: 3 per revolution (3 radial pistons) — Delivery strokes -> low injection torque, uniform load
Drive torque: 16 Nm Nm — Average drive torque (~1/9 of a comparable distributor pump)
Power intake: 3.8 kW kW — Power intake (2-litre engine, rated speed, 1350 bar, ~90% mech eff.); vs 2.5 kW distributor-type pump

Element cutout

Status: documented but NOT used by BMW — Holds intake valve open above ~1500 rpm and below 1/3 full-load injection volume, but causes unacceptable rail pressure pulsation and injected-volume fluctuation for BMW

Pressure control valve

Spring pressure: max. 100 bar bar — Spring-generated pressure (de-energised open)
Activation: PWM; magnetic force proportional to activation current — Activation
PWM frequency: 1 kHz kHz — PWM frequency (high enough to avoid armature-motion / pressure disturbance)
Start threshold: > 250 bar bar — Minimum rail pressure the DDE needs before it will start the engine (100 bar residual spring pressure assists restart)

Rail (high-pressure accumulator)

Arrangement: single rail — M57 rail arrangement
Bore diameter: ~ 9 mm mm — Longitudinal bore internal diameter
Throughput limiter: none — Throughput limiter absent (unlike other CR systems)

Rail pressure sensor

Diaphragm deformation: ~ 1 mm per 500 bar mm / bar — Diaphragm deformation
Bridge supply: 5 V V — Bridge supply voltage
Raw output: 0-70 mV mV — Raw bridge output (pressure-dependent)
Conditioned output: 0.5-4.5 V V — Conditioned output to DDE
Precision: 30 bar (~ +/-2% of full value) bar — Measuring precision (main operating range)
Fault behaviour: pressure control valve driven by the DDE emergency function — Sensor fault behaviour

Injector

Pull-in current: 20 A A — Start (pull-in) current, fast opening of 2/2 solenoid valve
Hold current: 12 A A — Hold current (smaller air gap allows reduction). Changeover 20A->12A
Changeover time: after max. 450 ms ms — Start->hold changeover time
Control + leakage: up to 50 mm3 per stroke mm3 — Control + leakage quantity (returned to tank)
Control-piston stroke: ~ 200 [mm] mm — CONFLICT: p.95 states control piston reaches upper limit after a stroke of approx. 200 mm. Physically implausible for an injector - almost certainly um (micrometres) or a mis-transcription of the scan. Verify against original figure.

Fuel heating / cooling (bimetal valve)

Full-cooling temp: >= 73 degC (+/- 3 degC) degC — 100% of return flows to tank via the fuel cooler
Direct-return temp: <= 63 degC (+/- 3 degC) degC — 60-80% of return goes directly to the filter; remainder to tank via the fuel cooler

Fuel cooler & distributor unit with throttle

Fuel cooler: air/heat exchanger with own air-guide ducting — Fuel cooler; external air removes heat from returned fuel
Distributor unit: 5-fold distributor unit with throttle — Under vehicle floor, left side, behind aux pump. Makes return-line fuel available (short-circuits return with supply) if pressure before the in-line EFP is too low

Injection-system comparison (CR vs distributor vs pump-nozzle)

CR pressure: 1350 bar bar — Common Rail injection pressure (vs 1800 bar radial-piston distributor pump, <2000 bar pump nozzle)
CR start-of-injection: any (flexible start-of-injection) — CR start-of-injection adjustment range (vs 20 deg KW 4-cyl / 15 deg KW 6-cyl distributor pump)
CR injection: multiple injection — CR injection process
CR principle: central piston pump linked to injector by an accumulator; electronic metering at the nozzle; HP pump drive NOT engine-synchronous; indirect needle activation — CR characterisation; favours large-capacity 6-/8-cyl and comfort

Injection concepts (pilot / main / post)

Documented stages: pre-injection (VE) + main injection (HE) only — S1 (09/98) documents only pre-injection (VE = Voreinspritzung) and main injection (HE = Haupteinspritzung) for the original M57 CR system (Figs 76-77)
Pre-injection function: pilot precedes main to give disturbance-free, low-noise combustion; small fuel-injection-rate peak (mm3/degKW) ahead of TDC — Pre-injection function
Post-injection: post-injection (NE) NOT documented for DDE 4.0/4.1 — CONFLICT/GAP: A distinct post-injection (NE = Nacheinspritzung) stage is not described in S1 pp.65-108. Do not attribute it to the original DDE 4.0/4.1 system without a later source (e.g. S2 M57TU1-TOP).

Common-rail system - summary of characteristics

Summary: injection pressure and timing selectable within wide limits, independent of operating point; reduced black smoke via high pressure (up to 1350 bar); reduced noise/emissions via pre-injection; HP generated by radial-piston pump, pressure set by pressure control valve; continuous closed-loop pressure measurement (sensor in distributor strip); injector with electromagnetic 2/2 solenoid valve